1. Field of the Invention
The present invention relates to an altimeter for measuring altitude based on pressure sampled at prescribed intervals and particularly to a highly portable altimeter.
2. Description of the Prior Art
This kind of portable altimeter is, for example, incorporated into the body of a wristwatch and has become widely publicized together with the recent increase in participation in outdoor activities. A block view of the essential parts of the configuration of this kind of related portable altimeter is shown in FIG. 27. The related portable altimeter shown in FIG. 27 is provided with a pressure sensor 100 for measuring pressure, an A/D converter 101 for converting an analog output for pressure from the pressure sensor 100 into a digital signal, a measurement controller 102 for controlling the pressure sensor 100 and the A/D converter 101, a pressure/altitude calculator 103 for calculating altitude based on pressure converted at the AID converter 101, a display altitude calculator 104 for subjecting the altitude calculated by the pressure/altitude calculator 103 to offset compensation, a switch 105 for carrying out an arbitrary instruction, a display panel 106 for displaying altitude, etc., a ROM 107 for storing programs for processing altitude measurements, a RAM 108 for temporarily storing measured values, etc., and a controller 109 for controlling each part.
A flowchart of an altitude measuring process for a related portable altimeter of this kind of configuration is shown in FIG. 28. As shown in FIG. 28, in this altitude measuring process, first, pressure is measured by the pressure sensor 100 (step S100) and altitude is calculated based on this pressure (step S101). This altitude calculation is carried out using equation (1) in the following so as to conform to the International Standard Atmosphere as specified by the International Civil Aviation Organization (ICAO).                               Altitude          ⁢                      xe2x80x83                    ⁢          in          ⁢                      xe2x80x83                    ⁢          an          ⁢                      xe2x80x83                    ⁢          ideal          ⁢                      xe2x80x83                    ⁢          gas          ⁢                      xe2x80x83                    ⁢                      (            m            )                          =                  44332          xc3x97                      {                          1              -                                                (                                      pressure                    ⁢                                          xe2x80x83                                        ⁢                                                                  (                        hPA                        )                                            /                      1013.25                                                        )                                                  0.1903                  }                                                                                        (                  Equation          ⁢                      xe2x80x83                    ⁢          1                )            
However, equation (1) is fulfilled for conditions where (a) an equation of state is fulfilled for an ideal gas, (b) where the pressure is 1013.25 hPa and the temperature is 15 degrees at a location 0 m above sea level, and (c) where temperature falls by 6.5 degrees for a rise of 1000 m. However, in reality, errors occur due to reasons such as, (d) the Earth""s atmosphere is not an ideal gas, (e) atmospheric pressure usually fluctuates and is therefore not fixed at 1013.25 hPa at 0 m above sea level, and (f) measuring errors occur within the pressure measuring system itself.
In order to resolve this error, an operation assigning an offset value to the altitude (hereinafter referred to as the xe2x80x9cideal gas altitudexe2x80x9d) calculated in accordance with the above equation is carried out at the display altitude calculator 104, a final displayed altitude (hereinafter referred to as xe2x80x9cdisplayed altitudexe2x80x9d) is decided upon (step S102), and this process ends (step 103). The decided displayed altitude is then displayed at the display panel 106. This offset value is a sum of the aforementioned errors, and is a correction value obtained by the user inputting the current altitude. This relationship is shown in the following equation (2).
displayed altitude (m)=offset value (m)+ideal gas altitude (m)xe2x80x83xe2x80x83(2)
However, it is of course preferable to provide an accurate way of measuring altitude without the user having to input current altitudes one by one to carry out offsetting. Altimeters have therefore also been proposed in the related art to resolve this kind of problem by identifying the presence or absence of actual changes in altitude.
In, for example, Japanese Patent Laid-open Publication No. Hei. 8-285582 and Japanese Patent Laid-open Publication No. Hei. 8-261755, it is proposed to provide, for example, a vibration sensor or a position sensor for detecting the presence or absence of movement of the altimeter and then maintain a fixed displayed altitude while ignoring changes in pressure when no movement of the altimeter is detected by these sensors (when the altimeter is not moving). Alternatively, it has also been proposed to obtain a change in altitude per unit of time, compare this altitude change with a prescribed reference change, and then determine that there has been a change in altitude only when this change in altitude exceeds a reference change in altitude (Please refer to Japanese Patent Laid-open No. 6-137976 and Japanese Patent Laid-open No. 6-501553, although the object of these reference examples differs from that of this application).
However, when movement detection is carried out as described in the former case, it is necessary to provide new sensors, etc., the cost of manufacturing the altimeter increases accordingly, and the device itself also becomes large. This is a major problem, particularly for portable altimeters where device miniaturization is sought.
Further, in the latter case where the altitude change is compared with a reference change, just one reference change can be set and there are therefore cases where there is no correspondence with actual changes in altitude. In other words, with this method, when the reference change is exceeded, it is determined immediately that there has been an actual change in altitude, and when the reference change is fallen below, it is immediately determined that there has actually been no change in altitude. However, in reality, there are also intermediate situations where there is actually no change in altitude when the reference change is exceeded, and also, on the contrary, cases where there has actually been a change in altitude when the reference change has been fallen below. If this kind of situation cannot be reliably determined, then measurement errors cannot be resolved.
In order to resolve the aforementioned problems, it is the object of the present invention to provide a portable altimeter capable of maintaining device portability, and precisely determine the presence or absence of actual changes in altitude to give highly accurate altitude measurements.
FIG. 1 is a block view of essential parts of a configuration for a portable altimeter of a first embodiment of the present invention. In FIG. 1, in addition to substantially the same basic structure as the related art, this portable altimeter is provided with a movement determining unit 12 for determining whether or not the altimeter is at a standstill or is moving by comparing an amount of change in altitude with a prescribed standstill threshold value 20 and a movement threshold value 30.
A portable altimeter of the present invention therefore comprises a pressure sensor for measuring pressure,
a pressure/altitude calculating unit for calculating altitude from pressure measured by the pressure sensor,
an altitude variation calculating unit for calculating a difference in altitude between the altitude calculated by the pressure/altitude calculating unit and another altitude for prior to calculation of the altitude, and
a movement determining unit constituted by a first determining unit for determining whether or not the altitude difference calculated by the altitude variation calculating unit is at a standstill, and a second determining unit for determining whether or not there is movement from the altitude difference calculated by the altitude variation calculating unit.
Determinations can therefore be made without using newly provided sensors etc. to determine whether the altimeter is moving or at a standstill, and measurement precision is improved.
In the present invention, the portable altimeter also has a movement duration timer for measuring a duration or number of durations occurring in a moving mode.
Moving states can therefore be measured, moving states can be more accurately determined, and measurement precision is improved.
The portable altimeter of the present invention also has a pressure gradient calculator for calculating changes in pressure occurring in standstill mode.
As a result, by being aware of changes in pressure occurring in standstill mode, it can be reliably determined whether changes in altitude are changes due to fluctuations in air pressure or changes due to movement, and measurement precision can therefore be improved.
A portable altimeter of the present invention also comprises a pressure sensor for measuring pressure,
a pressure/altitude calculating unit for calculating altitude from pressure measured by the pressure sensor,
an altitude variation calculating unit for calculating a difference in altitude between the altitude calculated by the pressure/altitude calculating unit and another altitude for prior to calculation of the altitude, and
a movement determining unit constituted by a determining unit for determining whether or not a transition is made from the altitude difference calculated by the altitude variation calculating unit and a movement duration timer for measuring a duration or number of durations occurring in a moving mode.
Moving states can therefore be measured, moving states can be more accurately determined, and measurement precision is improved.
A portable altimeter of the present invention also comprises a pressure sensor for measuring pressure,
a pressure/altitude calculating unit for calculating altitude from pressure measured by the pressure sensor,
an altitude variation calculating unit for calculating a difference in altitude between the altitude calculated by the pressure/altitude calculating unit and another altitude for prior to calculation of the altitude, and
a movement determining unit constituted by a determining unit for determining whether or not a transition is made from the altitude difference calculated by the altitude variation calculating unit, a movement duration timer for measuring a duration or number of durations occurring in a moving mode, and an atmospheric pressure tendency calculator for calculating changes in atmospheric pressure occurring in standstill mode.
As a result, precise measurements can be made without providing a standstill threshold value by combining changes in atmospheric pressure in standstill mode and changes in altitude.
The portable altimeter of the present invention can also be provided with a controller for calculating altitude based on pressure changing in accompaniment with actual changes in altitude to the exclusion of changes in pressure accompanying fluctuations in atmospheric pressure and making and displaying a time-altitude graph based on a relationship of the calculated altitude and time. The portable altimeter of the present invention can further be provided with a controller for calculating altitude based on pressure changing in accompaniment with actual changes in altitude to the exclusion of changes in pressure accompanying fluctuations in atmospheric pressure and making and displaying a time/estimated-altitude graph based on a relationship of the calculated altitude, and time. The portable altimeter of the present invention can also be provided with a controller for calculating altitude based on pressure changing in accompaniment with actual changes in altitude to the exclusion of changes in pressure accompanying fluctuations in atmospheric pressure, and making and displaying a rate of ascent/descent graph based on a relationship of a value for the obtained values by calculating a rate of ascent/descent from the calculated altitude, and time.
The present invention also provides an altitude measuring method for deciding a current altitude based on determination results of a movement determination step. Here, with a portable altimeter for measuring altitude based on pressure sampled in prescribed intervals,
standstill threshold values and movement threshold values are preset at reciprocal intervals as threshold values for an amount of change in pressure or altitude per prescribed period of time.
Then, the movement determination step, when it is determined from a past measurement that the altimeter is at a standstill, determines that the altitude remains at a standstill when an absolute value for a newly-obtained amount of change corresponds to an intermediate range between the standstill threshold value and the movement threshold value or falls below the standstill threshold value, determines that the altimeter has moved to a moving state when the absolute value for the amount of change exceeds the movement threshold value, and when it is determined from a past measurement that the altimeter is in a moving state, determines that the altimeter remains in a moving state when the newly obtained amount of change corresponds to the intermediate range or when the newly obtained amount of change exceeds the movement threshold value, and determines that the altimeter has moved to a standstill when the absolute value for the amount of change falls below the standstill threshold value.
At a movement determining unit 12, when the altimeter is in standstill mode, it is determined that the altimeter is maintaining a standstill mode when a new amount of change corresponds to an intermediate range between a standstill threshold value 20 and a movement threshold value 30, and it is determined that the altimeter has made a transition to a moving state when the amount of change rises above the movement threshold value 30. Further, when the altimeter is in moving mode, the altimeter is determined to still be moving when the new amount of change corresponds to the intermediate range or exceeds the movement threshold value 30, and the altimeter is determined to have made a transition to a standstill when the amount of change falls below the standstill threshold value 20. The current altitude is then decided based on the results of these determinations. In other words, no change is made to the current altitude when it is determined that the altimeter is at a standstill, but the current altitude is updated to a new altitude by a display altitude calculator 5 when it is determined that the altimeter is moving.
According to this process, determinations are made taking into consideration the situation up until that point in indeterminate cases where it is not clear whether the altimeter is at a standstill or moving and a much more accurate determination can therefore be achieved. The presence or absence of an actual change in altitude can therefore be precisely determined and highly accurate altitude measurements can be made. Further, the presence or absence of movement of the altimeter can be determined using this process without it being necessary to provide sensors such as vibration sensors or position sensors. The device is therefore prevented from becoming large and a small altimeter with a configuration suited to portable applications can be provided.
With the altitude measuring method of the present invention, when it is determined from a past measurement that the altimeter is in a moving state, the movement determination step determines that the altimeter has moved to a standstill when the newly obtained amount of change continues to be in excess of a prescribed value so as to correspond to the intermediate range.
The present invention also provides an altitude measuring method for deciding a current altitude based on determination results of a movement determination step. Here, with a portable altimeter for measuring altitude based on pressure sampled in prescribed intervals,
a movement threshold value is preset at a threshold value for an amount of change in pressure or altitude per prescribed period of time.
Then, in the movement determination step, when it is determined from a past measurement that the altimeter is at a standstill, it is determined that the altitude remains at a standstill when an absolute value for a newly-obtained amount of change falls below the movement threshold value, determines that the altimeter has moved to a moving state when the amount of change exceeds the movement threshold value, and when it is determined from a past measurement that the altimeter is in a moving state, determines that the altimeter remains in a moving state when the newly obtained amount of change exceeds the movement threshold value, and determines that the altimeter has moved to a standstill when the absolute value for the amount of change falls below the standstill threshold value but continues to be above the prescribed value.
In a further situation for a determination by the movement determining unit 12, just the movement threshold value 30 is set up and determinations can then be made taking into consideration continuous durations of the intermediate range, i.e. during moving mode, it is determined that the altimeter has become stationary when the newly obtained amount of change falls below the movement threshold value 30 and continues to do so for more than a prescribed value.
Precision is therefore improved as a result of this process. In particular, the amount of calculation required is reduced because the standstill threshold value 20 is not set and determination as to the magnitude of the amount of change with respect to the standstill threshold value 20 is not required.
The altitude measuring method of the present invention further comprises a tendency calculating step of obtaining a tendency value indicating a tendency of the amount of change of pressure by subjecting the amount of change in pressure obtained when the altimeter is determined to be at a standstill to prescribed statistical processing,
wherein a current altitude is decided based on determination results of the movement determination step and the tendency value obtained in the tendency calculating step.
When moving mode is temporarily set by the above process, and when the amount of change in atmospheric pressure or altitude continues for a long period to be within the intermediate range, the possibility that the altimeter is at a standstill is high. In this case, it can be determined when the amount of change continues to be within the intermediate range for more than a prescribed value that the altimeter has come to a standstill, and the mode can be changed to standstill mode.
According to this process, when moving mode is set, the amount of change continues to be in the intermediate range without reaching as far as the standstill threshold value 20, the altimeter is determined to be at a standstill, and the displayed altitude can be updated. In addition to the basic results stated above, and altitude precision is improved.
In addition to the above process, it is also possible to carry out correction taking into consideration the tendency of changes in atmospheric pressure occurring in standstill mode, i.e. a tendency value indicating the tendency of the amount of change of the atmospheric pressure is obtained based on the amount of change of atmospheric pressure obtained when the altimeter is in standstill mode and a current altitude is decided based on this tendency value.
According to this processing, the tendency of the change in atmospheric pressure in standstill mode is taken into consideration and correction of the displayed altitude is then carried out to give much more precise altitude measurements.
The altitude measuring method of the present invention can also comprise a calculating step for carrying out calculations based on atmospheric pressure changing in accompaniment with actual changes in altitude to the exclusion of the influence of atmospheric fluctuations, an altitude recording step for recording calculated altitudes acquired at prescribed times, and a graph making step for making a time/altitude graph based on a relationship of the recorded altitude, and time. The altitude measuring method of the present invention can also comprise a calculating step for carrying out calculations based on atmospheric pressure changing in accompaniment with actual changes in altitude to the exclusion of the influence of atmospheric fluctuations, an altitude recording step for recording calculated altitudes acquired at prescribed times, an estimation step for estimating and recording the recorded altitude, and a graph making step for making a time/estimated value graph based on a relationship of the estimated values, and time. The altitude measuring method of the present invention can also comprise a calculating step for carrying out calculations based on atmospheric pressure changing in accompaniment with actual changes in altitude to the exclusion of the influence of atmospheric fluctuations, an altitude recording step for recording calculated altitudes acquired at prescribed times, an ascent/descent rate calculating step for calculating and recording the ascent/descent rate from the recorded altitude, and a graph making step for making an ascent/descent rate graph based on a relationship of a value for the ascent/descent rate obtained through calculation, and time.